[R] Odp: Troubles with the format of dates

[Petr PIKAL]

Hi

r-help-bounces at r-project.org napsal dne 27.11.2008 14:20:17:

> Dear useRs,
> 
> I'm struggling again with date-related stuff: I am using R to draw water 

> levels at certain measuring 
> stations. My data comes as a tab-delimited text file and looks like 
this:
> 
> DATUM   P1   P2
> ...
> 2006-11-16       425.21   423.99 
> 2006-12-15     425.12   423.97 
> 2007-01-16       425.16   424.06 
> ...
> 
> (measurements started in July 2004 and still continue on a monthly or 
bi-weekly basis)
> 
> This is then plotted using this code:
> 
> a<-read.table("dummy_data.tab", sep="\t", header=TRUE, na.strings=c(0))
> x<-as.Date(a$DATUM)
> 
> plot(x, a$P1, axes=FALSE, xlim=c(as.Date("2004-07-01"), 
as.Date("2009-01-01")), 
> ylim=c(423,428), col="red", pch=15, type="o", ylab="Kote [m a.s.l.]", 
> main="Dummy Plot")
> points(x, a$P2, col="red", pch=17, type="o", lty="dotted")
> axis(2, at=423:428, tck=1, col="gray60")
> axis.Date(1, at=seq(as.Date("2004-07-01"), as.Date("2009-01-01"), 
> by="month"), labels=seq(as.Date("2004-07-01"), as.Date("2009-01-01"), 
> by="month"), tck=1, col="gray60")
> 
> So far, I've been using this type of date format (yyyy-mm-dd) because 
that was
> the only way I could 
> get  the whole thing to work when I started using R. However, living in 
> Switzerland, I would prefer 
> the dates to read 16.11.2006 i.e. dd.mm.yyyy or 16. Nov. 2006 
(preferably 
> using German names for 
> the months, if possible). 
> 
> I've used the chron package to convert my dates to day mon year (16 Nov 
2006, 
> with or without 
> spaces), i.e. I replaced the second line of code with:
> 
> x<-format(chron(as.character(a$DATUM), format="y-m-d", out.format="day 
mon year"))

Although I am not an expert in time/date functions it seems to me that you 
just want your labels to be in your preferred format. If it is the case

labels = format(seq(as.Date("2004-07-01"), as.Date("2009-01-01"), 
by="month"), "%d.%m.%Y")

in your call to axisDate can help you to achieve it.

Regards
Petr



> 
> but then I can't plot them any more, because as.Date() no longer is the 
> correct function and R gives 
> me an error saying there is an invalid xlim-value. Can someone please 
point me
> in the right 
> direction?
> 
> I could easily change the input data to be in dd.mm.yyyy format, if that 
helps.
> 
> Thanks for your help,
> 
> Kathi
> 
> 
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